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This paper proposes an on/off control of boost power factor correction (PFC) converters to improve the light-load efficiency in paralleled power supply units (PSUs) for servers. The proposed scheme operates the PFC stages of two paralleled PSUs alternately during one cycle of a 60-Hz ac input only at light loads. This improves the light-load efficiency without deteriorating the heavy-load efficiency by reducing load-independent losses such as capacitive turn-on and core losses. In addition, the proposed scheme alleviates the harmonic distortion by reducing the discontinuous conduction mode region. Experimental results from 1.6-kW PFC boost converters are shown to verify the proposed work.Index Terms-Boost converter, light-load efficiency, on/off control, paralleled power supply units (PSUs), power factor correction (PFC), servers.

This paper presents a new standby structure where a forward converter is integrated with a dc-dc phase-shift fullbridge (PSFB) converter for server power supplies. While a typical standby structure consists of an independent flyback converter, the proposed standby structure is integrated with one leg of the dc-dc PSFB converter. Its main advantages are that the voltage across a standby switch is clamped at the link voltage across the link capacitor and that the standby switch achieves zero-voltage switching over entire load range. The validity of the proposed standby structure is confirmed by the experimental results from 12 V/58 A for the dc-dc output prototype and 11.5 V/1.5 A for the standby output prototype.Index Terms-Forward, high efficiency, integration, server power supply, standby power, zero voltage switching.

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